From U.S. Pat. No. 5,386,493 it is known to vary reproduction rate of recorded sound while preserving pitch. In a game playing apparatus for example, the speed may be varied dependent on player interaction. Speed variations have an effect on the time points when respective parts of the recorded sound are needed. When variable speed is used, the time of replay becomes dependent on preceding changes of the replay speed. In contrast, with constant speed the time points would follow from the start of replay and the replay rate.
The effect on the time points has consequences upstream in the audio processing stream. When the audio samples are obtained by retrieving audio data or by decoding frame-encoded digital audio data that correspond to a constant replay speed, the time points of retrieving or decoding frames will have to be adapted to changes in the replay speed. These consequences are due to the fact that two different time bases are relevant: an original time base, which identifies locations in the stored audio data and which would apply without reproduction rate adaptation, and an adapted time base identifies the time points at which samples are rendered. A translation between these different time bases is needed to control operation.
Problems arise with this translation when the audio samples are buffered between the adaptation of the stream to change the reproduction rate and rendering of the audio samples. Changes in the time base that have been effected in front of the buffer emerge with a delay behind the buffer. When many changes of the reproduction rate occur in a brief time period the translation may become unreliable.